1. Field of the Invention
The present invention relates to a corrosion-resistant and abrasive wear-resistant composite material lining formed by centrifugal casting of sections of cylinders which are liable to corrosion and abrasion, which cylinders are used in plastics processing machines such as extruders and injection molding machines, slurry pumps, compression machines, pipes for slurry transportation, and many other similar applications.
2. Description of the Prior Art
Recently, there has been an increased demand for machinery for use in processing and transportation of fluids containing abrasive solids. For example, plastics processing machines for processing resins containing glass fiber, carbon fiber, asbestos or iron oxide; slurry pumps for fluid transportation of ore or coal; pipelines for transportation of slurries, and so forth have increasingly been demanded. Particularly, in cylinders for plastics processing machines, a metal material having corrosion-resistant and abrasive wear-resistance has been greatly desired in order to prevent corrosion from occurring during processing due to resins, additives incorporated into the resins, surface treating agents incorporated into the resins for the purpose of improving adhesion between the resins and fillers, and so forth, and to prevent abrasion due to reinforcing agents, fillers, or the like incorporated into the resins. Additionally, because fillers have been made recently with highly abrasive properties for effective utilization of resources and because an increased flame resistance of resins has been required due to the intensified application of UL Standards (UL Standards are defined in U.S.A.) associated with the increased imposition of safety regulations, corrosion-resistant and abrasive wear-resistance has increasingly been required for cylinder materials for use in plastics processing machines.
Heretofore known cylinders for plastics processing machines have been lined on the inner surface thereof with an alloy containing a large amount of iron (85% by weight or more), a nickel-cobalt based alloy or a cobalt based alloy. The former iron based alloy, however, is low in corrosion-resistance although the Vickers hardness (hereinafter referred to simply as "Hv") at room temperature in the lining state is 800 to 1000. The latter nickel-cobalt based alloy and cobalt based alloy have good corrosion-resistance, but their Hv at room temperature in the lining state is 550 to 750 and they are inferior in abrasive wear-resistance.
In order to eliminate the above defects, a composite material has been proposed in which tungsten carbide particles are dispersed in a nickel or cobalt based alloy. While the composite material has good corrosion-resistant and abrasive wear-resistance, it suffers from the following disadvantages.
The specific density of the reinforcing material, tungsten carbide, is about twice that of the nickel or cobalt based alloy matrix, and therefore, during the forming of a lining, the difference in centrifugal force resulting from the difference in specific density causes the tungsten carbide particles to be pressed more strongly than the alloy matrix against the side of the lining base material. Thus, the resulting lining is separated into a layer in contact with the lining base material in which tungsten carbide particles are dispersed densely and a layer apart from the lining base material in which no or almost no tungsten carbide particles are present. Thus in forming the corrosion-resistant and abrasive wear-resistant composite material, in which the tungsten carbide particles are dispersed in the nickel or cobalt based alloy matrix, on the inner surface of a cylinder, it is necessary to remove the said layer in which no or almost no tungsten carbide particles are present. Moreover, in controlling the boundary between the layer containing the tungsten carbide particles and the layer free from tungsten carbide particles in the vicinity of the predetermined depth from the inner surface of the lining, it is necessary to carry out the lining operation under strictly controlled conditions.
Furthermore, since the tungsten carbide particles congregate at the interface between the lining base material and the lining layer, the adhesion strength between the lining base material and the lining layer is low and the lining layer is easily stripped off. The tungsten carbide particles-containing layer per se has good abrasive wear-resistance but has a tendency to wear away any metal material which may come into contact therewith such as a screw. In addition, tungsten is expensive and its supply is uncertain.